import java.util.LinkedList;
import java.util.Objects;
import java.util.Queue;

public class BinaryTree {
    static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }
    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode A=new TreeNode('A');
        TreeNode B=new TreeNode('B');
        TreeNode C=new TreeNode('C');
        TreeNode D=new TreeNode('D');
        TreeNode E=new TreeNode('E');
        TreeNode F=new TreeNode('F');
        TreeNode G=new TreeNode('G');
        A.left=B;
        A.right=C;
        B.left=D;
        B.right=E;
        C.left=F;
        C.right=G;

        return A;
    }

    // 前序遍历
    public void preOrder(TreeNode root) {
        if(root==null){
            return;
        }
        System.out.println(root.val);
        postOrder(root.left);
        postOrder(root.right);
    }

    // 中序遍历
    public void inOrder(TreeNode root) {
        if(root==null){
            return;
        }
        inOrder(root.left);
        System.out.print(root.val+" ");
        inOrder(root.right);
    }

    // 后序遍历
    public void postOrder(TreeNode root) {
        if(root==null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val+" ");
    }

    public static int nodeSize=0;

    /**
     * 获取树中节点的个数：遍历思路
     */
    public int size(TreeNode root) {
        if(root == null) {
            return 0;
        }
        nodeSize++;
        size(root.left);
        size(root.right);
        return nodeSize;
    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    public int size2(TreeNode root) {
        if(root == null) {
            return 0;
        }
        int tmp = size2(root.left)+size2(root.right)+1;
        return tmp;
    }


    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafSize = 0;

   public int getLeafNodeCount1(TreeNode root) {
       if(root==null){
           return 0;
       }
       if(root.left==null&&root.right==null){
           return 1;
       }
       return getLeafNodeCount1(root.left)+getLeafNodeCount1(root.right);
    }

    /*
     获取叶子节点的个数：子问题
     */
    public int getLeafNodeCount2(TreeNode root) {
        if(root==null){
            return 0;
        }
        if(root.left==null&&root.right==null){
            leafSize++;
        }
        getLeafNodeCount2(root.right);
        getLeafNodeCount2(root.left);
        return leafSize;
    }

    /*
    获取第K层节点的个数
     */
    public int getKLevelNodeCount(TreeNode root, int k) {
        if(root==null||k<=0){
            return 0;
        }
        if(k==1){
            return 1;
        }
        int temp=getKLevelNodeCount(root.left,k-1)+ getKLevelNodeCount(root.right,k-1);
        return temp;
    }

    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    public int getHeight(TreeNode root) {
        if(root==null){
            return 0;
        }
        int leftHeight=getHeight(root.left);
        int rightHeight=getHeight(root.right);
        return leftHeight>rightHeight?leftHeight+1:rightHeight+1;
    }


    // 检测值为value的元素是否存在
    public TreeNode find(TreeNode root, char val) {
        if(root==null){
            return null;
        }
        if(root.val==val){
            return root;
        }
        TreeNode ret1=find(root.left,val);
        if(ret1!=null){
            return ret1;
        }
        TreeNode ret2=find(root.right,val);
        if(ret2!=null){
            return ret2;
        }
        return null;
    }

    //层序遍历
    public void levelOrder(TreeNode root) {
        if(root==null){
            return;
        }
        Queue<TreeNode>qu=new LinkedList<>();
        qu.offer(root);
        while(!qu.isEmpty()){
            TreeNode cur=qu.poll();
            System.out.print(cur.val+" ");
            if(cur.left!=null){
                qu.offer(cur.left);
            }
            if(cur.right!=null){
                qu.offer(cur.right);
            }
        }
    }


    // 判断一棵树是不是完全二叉树
    public boolean isCompleteTree(TreeNode root) {
        if(root==null){
            return true;
        }
        Queue<TreeNode>qu=new LinkedList<>();
        qu.offer(root);
        while (!qu.isEmpty()) {
            TreeNode cur = qu.poll();
            if (cur != null) {
                qu.offer(cur.left);
                qu.offer(cur.right);
            } else {
                break;
            }
        }
            while (!qu.isEmpty()) {
                TreeNode pop = qu.poll();
                if(pop != null) {
                    return false;
                }
            }
        return true;
    }
    //翻转二叉树
    public TreeNode invertTree(TreeNode root) {
        if(root==null){
            return null;
        }
        TreeNode left=invertTree(root.left);
        TreeNode right=invertTree(root.right);
        root.left=right;
        root.right=left;
        return root;
    }
}

